For hundreds of thousands of refugees like Souad Omar Mousa the rain that fell yesterday in the Darfur region of Sudan is something to dread.

"If I was in my village, I would welcome it," she said. "But here we are exposed." Home for Mrs Mousa is now the Kalma camp, near Nyala, one of hundreds scattered throughout Darfur. Refugees live under straw matting or in the open.

In what the United Nations describes as the world's worst humanitarian disaster, the arrival of the rains means that life for the refugees will become even more grim and the death toll will almost certainly rise.

About 30,000 are estimated to have been killed in the last year, victims of a government-armed militia that has terrorised and destroyed villages throughout Darfur, where 1.2 million have been displaced, with a further 100,000 taking refuge in neighbouring Chad.

A UN official who has travelled extensively throughout the region said yesterday: "If you go 1,000km from here to Chad you will not see a single village intact."

During a three-hour flight over Darfur, hundreds of blackened and scorched villages were starkly visible against the red desert. Mrs Mousa walked for three days to reach Kalma after the Janjaweed militia attacked her village, Shatee, west of the Mara mountains, two months ago.

"They came at dawn, at 4am. They came on horses, donkeys, camels and Land Cruisers. They burnt the houses and killed the men and many of the male children. I don't know if my husband is alive or dead."

She fled with her four sons and three daughters, but one of her children, Omar Abdul Rahin, seven, died on the way.

The refugees claim the government is engaged in ethnic cleansing, using the Arab Janjaweed to force out black Africans. The Sudanese government denies the charge and blames rebel forces rather than the militia.

The government has allowed few journalists into Darfur to see what is happening.

Kalma is one of the better camps because of the presence of Médecins sans Frontières, the international medical relief charity. But the death toll is still very high, way above what aid agencies regard as crisis point. There are about 10 deaths a day, most of them children.

Tom Quinn, the MSF medical team leader in the camp, said he went to five graveyards ringing the camp last week and counted 131 mounds of earth, gauging the size of the body by the length of the mound. "Of the 131, only 13 were adults," he said.

There was a desperate need for aid, especially plastic sheeting to provide some protection from the rain. He complained of obstruction by the government, saying that 30 tonnes of medicine has been lying at Port Sudan since early May.

The rain, he added, was another concern: "This whole area will be flooded." Even if the camp survived there would be pollution, malnutrition and disease.

A British delegation led by the international development secretary, Hilary Benn, yesterday had a confrontation with the governor of South Darfur, General Hamid Mussa, who insisted that the instability in the region should be blamed mainly on rebel forces. Mr Benn questioned him about allegations that the government had provided the militia with weapons. One of Gen Mussa's ministers replied that weapons were readily available throughout Sudan because of wars in neighbouring countries.

The camps throughout Darfur range from places like Kalma, which at least has medical facilities, to Meshtel in the north of the country in which refugees are living in the open and are forcibly removed at frequent intervals by the government. Meshtel is beside a river which will almost certainly flood when the rains arrive.

The refugees arriving at all the camps tell of fresh attacks. Aisha Yunis Suleiman, 35, reached the Kalma camp five days ago from Mugdi. She said her village had suffered an aerial bombardment in which her husband had been killed and that the militia had gone into the village immediately afterwards. Asked who had been responsible she said: "The government." She would only return to the village "when it is secure".

Mrs Mousa too will not go back until she is sure there is peace. She was prepared to risk the devastation and possible death from the rains because, she said: "There is a bigger risk of dying in the village."